The present invention relates to the field of laser systems, in particular to a frequency tunable laser system for use in an optical measuring system. The present invention further relates to a method for tuning a frequency tunable laser system.
Optical measuring systems may be used to perform measurements of optical properties as a function of optical frequency. One example of an optical measuring system may employ an optical sensing element e.g. comprising a Fiber Bragg Grating (FBG) or ring resonator or Fabry-Perot sensor. Such an optical sensing element may exhibit a spectral signature that varies as a function of a physical parameter influencing the sensing element. In order to use the optical sensing element to quantify the physical parameter, a measurement of the spectral signature of the optical sensing element is desired.
Measuring the spectral signature of an optical sensing element may comprise probing the optical sensing element with a varying narrowband optical signal and recording the spectral response of the sensing element. The varying narrowband optical signal may be generated by passing a broadband optical signal through a narrowband scanning filter. Alternatively, the narrowband optical signal may be directly generated, e.g. by a tunable narrowband laser diode. In a scan, the optical frequency of the narrowband optical signal may be varied through a range of probing frequencies and a resulting response of the optical sensing element may be recorded. In order to accurately reconstruct the spectral signature of the sensing element, it is desired to measure and/or calculate the optical frequency of the narrowband optical signal, e.g. during the scan or afterwards.
US2005/0134861 discloses a method for determining optical wavelengths, such as the Bragg wavelengths of an FBG sensor array. Wavelength-swept light having a characteristic spectrum is swept over a bandwidth and is applied to an interference filter. The interference filter produces an optical spectrum having one or more reference peaks that are identifiable because of the characteristic spectrum. The optical spectrum is converted into electrical signals having at least one electrical signal that is identifiable because of the characteristic spectrum. The identifiable electrical signal is used by a signal processor as an absolute wavelength reference.
There is a desire for a frequency tunable laser system of simpler design.